Cationic biocide susceptibility and tolerance-associated genes in clinical, environmental, and commensal Enterococcus isolates

Abstract

Abstract Enterococcus spp. are important etiological agents of both healthcare associated and community-acquired infections, necessitating effective antisepsis and disinfection strategies to limit their transmission. This study aimed to evaluate the susceptibility of Enterococcus isolates from clinical, environmental, and commensal sources to benzalkonium chloride (BCC) and chlorhexidine digluconate (CHX), and to investigate their association with selected efflux-associated genes. A total of 520 specimens were collected from clinical settings, hospital environments, and faecal samples obtained from healthy individuals. From these, 120 Enterococcus isolates were recovered and subjected to antimicrobial susceptibility testing. Minimum inhibitory concentrations (MICs) for CHX and BCC were determined using an agar dilution method under standardized laboratory conditions. Biofilm formation was quantified using a microtiter plate assay, and the efflux pump genes emeA , efrA , and efrB were detected by PCR. Clinical isolates demonstrated significantly higher resistance to gentamicin and ciprofloxacin, along with reduced susceptibility to CHX and BCC, as reflected by higher MIC₅₀ and MIC₉₀ values. Biofilm formation was observed in 66.7% of isolates and was significantly more prevalent among clinical strains. Isolates harboring efflux pump genes exhibited higher MIC₉₀ values for both biocides, and efrAB and emeA were strongly associated with gentamicin resistance. Overall, clinical Enterococcus isolates exhibited higher antimicrobial resistance, enhanced biofilm-forming capacity, and reduced susceptibility to CHX and BCC compared with environmental and commensal isolates. These findings suggest a potential role of efflux-mediated mechanisms in reduced biocide susceptibility and antibiotic resistance.